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Multi-zone Heat Pump Condensing Units
MULTI-ZONE CONDENSER SEQUENCE OF OPERATION
EMI America Series multi-zone heat pump
condensers are designed to operate with
EMI America Series indoor air handlers.
Both the condenser (outdoor unit) and
evaporator (indoor unit) have a high Volt
service connection. Each is to be indepen-
dently connected to the electrical service
panel. (See the unit name plate for the cor-
rect breaker type and size). The outdoor
and indoor units are also connected to each
other through a low Volt interconnect wiring.
A 24V transformer located in the indoor unit
provides the low Volt power source.
The S & T series (S2HA, T2HA, T3HA &
T4HA) is a limited range heat pumps that
will provide comfort cooling or heat pump
operation operate at an outdoor tempera
-
ture range between 35°F and 115°F for
cooling, 35°F and 75°F for (heat pump)
heating. The outdoor unit is equipped
with a thermostat that will switch off the
condenser when temperature falls below
35°F. For heat pump mode the condenser
operation will cease and then switch on
the indoor electric heat. For cooling mode,
condenser operation will cease.
The S & T series (S2HA, T2HA, T3HA &
T4HA) limited range heat pump condens
-
ers are designed to operate as a single
stage cooling, two stage heating unit. For
full operation the unit should be matched
with an appropriate EMI indoor unit with
electric heat and unit mounted controls or
a wall mounted thermostat.
For two stage heating operation the indoor
unit must be equipped with an electric strip
heater.
See the instruction manual for the indoor
unit on the selection of the proper thermo
-
stat for the system.
Condenser Operation:
The transformer located in the indoor unit
provides 24V, low-Volt control power to the
condenser (outdoor unit). This can be mea
-
sured across low-Volt terminals “R” and “C”.
Heat pump condensers utilize a reversing
valve to provide reverse cycle operation.
Therefore the outdoor unit will act as ei
-
ther a condenser or an evaporator there-
by providing comfort cooling or heating to
the indoor space. The reversing valve is
energized in cooling. Should the valve fail
to actuate, the system will default to the
heating mode of operation.
Cooling operation, Multi-zone Heat
Pump:
Cooling mode operation requires that the
control (either unit mount or remote wall
mount thermostat) make a connection be
-
tween low-
Volt terminals “R” and “Y” along
with “R” and “O”. When the indoor control
is placed in cooling mode, with the set point
temperature below the room temperature,
the reversing valve will energize (R & O)
along with the compressor and outdoor fan
(R & Y). When the indoor control is satis
-
fied and the room temperature falls below
the set temperature, the compressor and
fan will de-energize. The EMI indoor unit
is equipped with an anti-short cycle timer
(ASCT) will prevent the compressor from
re-starting for three minutes.
When the outdoor temperature falls below
35°F, compressor operation will cease.
Heating operation, Multi-zone Heat
Pump:
Heating mode operation requires that the
control (either unit mount or remote wall
mount thermostat) make a connection
between low-Volt terminals “R” and “Y”
only. When the indoor control is placed
in heating mode, with the set point tem-
perature above room temperature, the
compressor and outdoor fan (R & Y) will
energize. When the indoor control is satis-
fied and the room temperature rises above
the set temperature, the compressor and
fan will de-energize. The EMI indoor unit
is equipped with an anti-short cycle timer
(ASCT) will prevent the compressor from
re-starting for three minutes.